1. Field of the Invention
The present invention relates to a method of correcting misalignment of optical axes caused by zooming in an image pickup apparatus.
In particular, the present invention relates to an image pickup apparatus having at least one of a pan mechanism and a tilt mechanism, for example, an image pickup apparatus capable of correcting a center shift of a captured image generated due to misalignment of optical axes of an image pickup lens system caused by zooming when zooming is optically performed.
2. Description of the Related Art
In recent years, a high power, high image-quality image pickup apparatus has been developed. Ideally, if optical axes of all lenses in a lens system are aligned with each other, a center shift of a screen caused by zooming does not occur. Hence, a center object at a wide-angle end would not be shifted from a center object at a telephoto end. Also, a center shift does not occur at an intermediate position.
However, a center shift may actually occur during zooming due to mechanical variation, such as decentration of lens groups, or a deviation between mounting positions of a lens and an image pickup element.
Ideally, when an object 2 located at the center of a screen 1 is zoomed as shown in FIG. 5A, the object 2 should be located at the center of a screen 3. However, due to the above-mentioned reasons, the object 2 may be shifted from the center of the screen 3 because of zooming as shown in FIG. 5B.
In a monitoring image pickup apparatus and an industrial image pickup apparatus, pan and tilt operations are performed by using a camera platform. Also, in order to capture an image at a desired position in an enlarged manner, a lens having a high-power zoom mechanism may be used. Thus, a center shift of a screen caused by zooming has been a bottleneck in recent years.
To reduce the center shift, for example, processing accuracy of a lens or a member belonging to the lens may be increased, or such a member may be adjusted after assembly. However, either method is troublesome work and increases the manufacturing cost.
In light of this, Japanese Patent Laid-Open No. 9-27926 discloses a method for correcting the center shift, in which an extraction position from the image pickup element is shifted to correct the center shift. Japanese Patent Laid-Open No. 2006-191181 discloses that an optical-path correction optical system for image stabilization is also used for correcting the center shift during zooming.
However, when the center shift is corrected by shifting the extraction position from the image pickup element as disclosed in the Japanese Patent Laid-Open No. 9-27926, an image to be captured utilizes only a part of effective pixels of the image pickup element, and hence, image quality may be deteriorated.
When the correction optical system for image stabilization is also used for correcting the center shift as disclosed in Japanese Patent Laid-Open No. 2006-191181, the image quality is not deteriorated. However, since a part of a vibration angle of the optical system for image stabilization is used for center-shift correction, an image stabilization effect and a center-shift correction effect may not be sufficiently provided.